1. Field of the Invention
This invention relates to an information terminal device having a function of backing up encrypted content data to an external storage medium and a content backup method which performs the above backup operation.
2. Description of the Related Art
In the Open Mobile Alliance (OMA), Digital Rights. Management Version 2 (DRM 2) has released a specification for managing the right to decrypt or use encrypted content.
According to the above specification, content and a rights object containing information indicating the right of decrypting the content and key information are distributed separately. The rights object is associated with the content by use of an ID (ContentID) attached to the content. Decrypting of the content is performed by referring to the correct rights object. The rights object is independently bound with the terminal or bound with the terminal and user identity module (UIM) which the user has, and a specification which prevents decryption on an other terminal or the like is defined in the rights object.
The backup of the content is defined as “Off device storage of contents and rights objects” section in the above specification and requirements that the right object which requires the status management for the stateful rights should not be output or the like are defined, however, the right object which does not requires the status management for the rights, e.g. stateless rights can be output or the like. However, in the above specification, technical information about the concrete storage method is not defined.
The content and rights objects can be contained in different files in a file structural form and are separated on a file system. Therefore, in order to restore content and rights objects from an external storage medium in which plural sets of content and rights objects are backed up to an information terminal device, it becomes necessary to search for an ID which is used to recognize the correspondence relationship between the content and the rights objects.
Further, it is required to make an attempt to parse and check whether or not the rights objects backed up in the external storage device or medium are bound with the information terminal device into which the rights objects are to be restored.
In a case where single content is separately acquired together with different rights objects, the capacity of the external storage device or medium is uselessly suppressed if the above content is repetitively stored in the external storage device.
Under this condition, it is desired to efficiently back up content data and rights data such as content and rights objects in OMA DRM 2.